1. Field of the Invention
The present invention relates to utilizing a fob to direct a user to a vehicle using GPS coordinates.
2. Background Art
Car locating systems having a portable GPS receiver carried by the vehicle user and a car-mounted GPS receiver have been proposed. Typically, a GPS-derived location of the car when it is parked is downloaded to the portable receiver as a waypoint. Later, when the user wants to return to the vehicle, the portable receiver is actuated to determine its current location and to then provide a direction and distance to the vehicle waypoint.
Atmospheric, noise, timing, and any number of other conditions, as one having ordinary skill in the art will appreciate, can influence the ability of the fob to direct the user to the previously stored waypoint. The follow list provides a range of distance variations that may be introduced to GPS signals: ionosphere 0-30 meters; troposphere 0-30 meters; measurement noise 0-10 meters; ephemeris data 1-5 meters; clock drift 0-1.5 meters; and multipath 0-1 meters.
These variables, without correction, cause the fob to provide inaccurate directionality information with respect to the stored waypoint. If the fob is deactivated or otherwise prevented from monitoring/receiving GPS coordinates, the fob loses its ability to correct itself relative to the previously stored waypoint. Thereafter, the fob is unable to accurately locate the waypoint such that subsequently GPS calculations based on the previously stored coordinates tend to be relatively inaccurate.
These inaccuracies may be further exacerbated as a function of distance to the vehicle. If the user is relatively close to the vehicle and the fob determines an inaccurate direction to the vehicle due to the varying GPS coordinates, the user can be directed away from the vehicle or in a direction that is unlikely to result in the user locating the vehicle. If the user is relatively far from the vehicle, the errors are less important due to the distance that must be traveled to reach the vehicle.